The present invention relates generally to a method and device for detecting vehicle driver fatigue in driving and for generating an alarm for the driver to rest. More particularly, the invention relates to a method and device for measuring a period of driving time in which the driver becomes fatigued and for giving an alarm to the driver to indicate that it is time to take a rest.
It has been well known that it is recommendable to take a rest every two or two and a half hours driving for refreshing oneself and for recovering from driving fatigue. It is especially necessary for the driver to take a rest in driving a relatively long time.
There have been developed and proposed various alarm devices for generating an alarm for resting. For example, published Japanese Utility Model (Tokko Sho) No. 48-15104 shows an alarm device which is associated with a tachograph to produce an alarm at a given time. On the other hand, unexamined Japanese Utility Model Publication (Jikkai Sho) No. 51-156878 shows a device for displaying a required resting period of time depending on a driving period.
Since the foregoing devices are adapted to provide the alarm for the vehicle at certain fixed timing intervals, the timing to generate the alarm does not always correspond to the driver's fatigue. For example, if the driver takes a rest before the fixed time therefor or if a driving condition is significantly varied, the fixed timing for providing the alarm will not correspond to the driver's fatigue.
To improve the above-mentioned defect, unexamined Japanese Utility Model (Tokkai Sho) No. 52-13232 shows another alarm device which counts a clock signal to detect the timing to give the alarm. In this device, the timing is detected by analog processing of the clock signal. Therefore, if the driving time is relatively long, e.g., 3 hours, the analog processing of the clock signal must be continued for a long time and requires a substantially large capacity of an analog arithmetical element. Further, by accumulation of error in measurement, the accuracy of detecting the timing by calculation will be lowered.